We’ve talked a lot about molecules and hoses. But that doesn’t help when we really want to talk about flight.
Let’s change our examples up a bit and add some numbers to make them clearer. Pretend we have an airplane wing flying at about 50 miles per hour through the same substances as before, water and oil.
Doing the math (which includes the density, speed, and viscosity of the flow) our Reynolds number for “flying” through water is around 6.8 million. This is pretty high.
If we’re flying through the oil, our Reynolds number drops to 120,000. That’s way smaller!
And if we tried to fly through honey (with a viscosity 2,000x that of water), our Re would be 3,400. Tiny, comparatively.
We don’t fly through water though (despite how high humidity feels). So how does this help us talk about bees?
We now have a visual of how flows behave at different Reynolds numbers. We can see where a bee would land on that range.
A single bee wing is about 9 millimeters long (let’s assume 4.5 mm for the cross-section), and bees can fly up to 20 miles per hour.
That means a bee flying through air has a Reynolds number of 2750. That’s even lower than our airplane wing flying through honey.
Remember, the Reynolds number lets us compare different flows without needing to take any sizes or conditions into account—any two flows at the same number will have the same physics, regardless of the actual substance. That’s the beauty of it.
So, math aside, what does this mean?
I’ll restate what I said at the very beginning: bees are so tiny, and flying at such low speeds, that the forces due to the friction of all those little air molecules are almost equivalent to the forces from the molecules moving.
The airflow has just barely enough energy to overcome that friction. At that point the bee isn’t really flying—it’s much more like paddling through honey. Poetic, isn’t it?
There are a couple other reasons why saying bees “shouldn’t” be able to fly is bogus:
- Bees don’t glide on their wings like birds and airplanes do. They have four wings and move them in a complex, high-speed pattern that has more similarities to helicopter flight than fixed-wing aircraft flight. (Helicopters shouldn’t be able to fly either, but I digress.)
- Part of this complex pattern includes constantly changing the angle of their wings. This creates tiny little pockets of low pressure, and the difference in pressure between the top and bottom of the wing is what creates lift.
Now you know—bees are perfectly capable of flight, the physics backs them up, and they’re actually pretty good at it, thanks for asking.
I’ll end by asking for a favor: next time you hear someone repeat that stupid line, tell them it’s false. Hopefully you’ll remember a fact or two from here you can sprinkle in.
Please, for my sake.